A device is known from the Swiss patent (CH-PS 574 144), in which a card-like or tape-like payment-means contains a multitude of units of values in form of mechanically readable optical markings which, to give an example, can be holograms or diffraction screens. For cashless payments for goods or services rendered, the payment-means are devaluated step-by-step in accordance with the amount to be paid, namely in that the markings are thermically erased by means of a transparent heating element. A reading-light-beam is directed through the transparent heating element to a marking, the marking is then checked by means of light sensing elements for genuineness, is then erased and by means of signals obtained from the light sensing elements, a check is performed whether the marking has been actually erased.
Furthermore, a method for the production of a document is known from Swiss patent CH-PS 594 935, in the case of which a multitude of optical markings, which for example can be holograms or diffraction screens, are recorded on a carrier and in which, for the purpose of writing in a code, selected markings are then subsequently erased. The erasing of the markings takes place by means of heating elements, which consist of a resistance layer which, in turn, has been applied onto a substrate.
Hannan, U.S. Pat. No. 4,108,367, although having some similarities with the present invention, does not attain the objects of the present invention. Both the light source and the light sensors postcoupled to the comparator are disposed on one side of the carrier. The output signals of the light sensors do not have respective opposite polarities when a marking is erased, nor is the reading means operable during the erasure process, as the light rays are interrupted by the erasing head. The duration of the erasure process is determined by the delay of the erasure means in starting and terminating erasures, and is independent of the fact whether or not an adequate erasure has been obtained.
The German laid open patent specification DE 26 59 639 teaches reading means and an erasure head disposed on the same side of a document, and therefore teaches away from the present invention.
Schaffer, U.S. Pat. No. 2,975,282 teaches how to copy information from a credit card by means of a lamp onto one side of a sales ticket, and is not relevant to the present invention.
Hickey et al, U.S. Pat. No. 3,921,969 is not relevant other than documenting the fact that a moving or transportation device for documents is known.
It should be added that British Pat. No. 1 502 460 is equivalent to Swiss Pat. No. 574,144, and that U.S. Pat. No. 4,143,810 is equivalent to Swiss Pat. No. 594,935.